@btnW: 150px;
@btnH: 70px;
@paddingL: 6px;
@time: 0.6s;
.button {
  display: inline-block;
  line-height: 0;
  cursor: pointer;
}
.btnInner {
  transition: all @time ease-in-out;
  line-height: 0;
  display: inline-block;
  position: relative;
  height: @btnH;
  width: @btnW;
  border-radius: 100px;
  box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.4), 0 0 3px rgba(0, 0, 0, 0.6);
  overflow: hidden;
}
.bg {
  transition: all @time ease-in-out;
  display: inline-block;
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  background: -webkit-linear-gradient(top, #2bcef7 0%, #1b639e 100%);
  background: linear-gradient(to bottom, #2bcef7 0%, #1b639e 100%);
  opacity: 1;
  &.bg2 {
    background: -webkit-linear-gradient(top, #043789 30%, #020914 100%);
    background: linear-gradient(to bottom, #043789 30%, #020914 100%);
    opacity: 0;
  }
}
.sun {
  transition: all @time cubic-bezier(0.42, -0.34, 0.56, 1.4);
  transition-delay: @time * 0.5;
  position: absolute;
  width: @btnH * 0.18;
  height: @btnH * 0.18;
  top: 12%;
  left: 48%;
  border-radius: 200px;
  background: #fef495;
  &.sun2 {
    top: 120%;
    opacity: 0.15;
  }
}
.circle {
  transition: all @time ease-in-out;
  position: absolute;
  z-index: 2;
  overflow: hidden;
  width: @btnH - @paddingL - @paddingL;
  height: @btnH - @paddingL - @paddingL;
  top: @paddingL;
  left: @paddingL;
  background: #fff4ac;
  border-radius: 100px;
  box-shadow: 0px 0px 5px rgba(0, 0, 0, 0.6),
    inset -0.5px -1px 3px rgba(0, 0, 0, 0.6),
    inset 1px 1px 3px rgba(255, 255, 255, 0.5);
  .circleNight {
    transition: all @time ease-in-out;
    position: absolute;
    top: 0;
    left: 120%;
    width: 100%;
    height: 100%;
    border-radius: 100px;
    background: #709ed1;
    box-shadow: 0px 0px 5px rgba(0, 0, 0, 0.6),
      inset -0.5px -1px 2px rgba(0, 0, 0, 0.6),
      inset 1px 1px 2px rgba(255, 255, 255, 0.8);
  }
  .crater {
    position: absolute;
    width: 25%;
    height: 25%;
    top: 12%;
    left: 44%;
    border-radius: 100px;
    background: #3f557d;
    &.crater2 {
      width: 34%;
      height: 34%;
      top: 42%;
      left: 16%;
    }
    &.crater3 {
      width: 19%;
      height: 19%;
      top: 62%;
      left: 63%;
    }
  }
}
.stars {
  transition: all @time * 0.5 ease-in-out;
  transition-delay: @time * 0.3;
  transform: scale(1.2);
  opacity: 0;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  .star {
    display: inline-block;
    position: absolute;
    left: 28%;
    top: 2%;
    width: 2px;
    opacity: 0.6;
    &.star2 {
      left: 13%;
      top: 20%;
      opacity: 0.8;
    }
    &.star3 {
      left: 22%;
      top: 35%;
      width: 4px;
      opacity: 0.9;
    }
    &.star4 {
      left: 27%;
      top: 27%;
    }
    &.star5 {
      left: 32%;
      top: 15%;
    }
    &.star6 {
      left: 51%;
      top: 7%;
      opacity: 0.8;
    }
    &.star7 {
      left: 70%;
      top: 0%;
    }
    &.star8 {
      left: 92%;
      top: 13%;
    }
    &.star9 {
      left: 48%;
      top: 33%;
    }
  }
}
.mountains {
  position: absolute;
  width: 100%;
  height: 100%;
  left: 0;
  top: 0;
  .mountain {
    position: absolute;
    width: 103%;
    top: 0%;
    left: -1%;
    transition: all @time ease-in-out;
  }
  .mountain1 {
    transition-delay: @time * 0.1;
  }
  .mountain2 {
    transition-delay: @time * 0.2;
  }
  .mountain3 {
    transition-delay: @time * 0.3;
  }
  .mountain4 {
    top: 100%;
    transition-delay: @time * 0.3;
  }
  .mountain5 {
    top: 100%;
    transition-delay: @time * 0.2;
  }
  .mountain6 {
    top: 100%;
    left: -18%;
    transition-delay: @time * 0.1;
  }
}
.grounds {
  position: absolute;
  width: 100%;
  height: 23%;
  left: 0;
  bottom: 0;
  background: #fff;
  .ground {
    transition: all @time ease-in-out;
    position: absolute;
    width: 100%;
    height: 100%;
    box-shadow: 0 0 3px rgba(0, 0, 0, 0.2);
    &.ground1 {
      background: -webkit-linear-gradient(top, #f4b067 0%, #fef493 100%);
      background: linear-gradient(to bottom, #f4b067 0%, #fef493 100%);
      opacity: 1;
    }
    &.ground2 {
      background: -webkit-linear-gradient(top, #162b7a 0%, #047aec 70%);
      background: linear-gradient(to bottom, #162b7a 0%, #047aec 70%);
      opacity: 0;
    }
  }
}
.night {
  .bg {
    opacity: 0;
    &.bg2 {
      opacity: 1;
    }
  }
  .circle {
    left: @btnW - @btnH + @paddingL;
    .circleNight {
      left: 0;
    }
    .mountain6 {
      top: 12%;
    }
  }
  .stars {
    transform: scale(1);
    opacity: 1;
  }
  .mountains {
    .mountain1 {
      transition-delay: @time * 0.3;
      top: 100%;
    }
    .mountain2 {
      top: 100%;
    }
    .mountain3 {
      transition-delay: @time * 0.1;
      top: 100%;
    }
    .mountain4 {
      transition-delay: @time * 0.1;
      top: -5%;
    }
    .mountain5 {
      top: -5%;
    }
    .mountain6 {
      transition-delay: @time * 0.3;
      top: 10%;
    }
  }
  .grounds {
    .ground1 {
      opacity: 0;
    }
    .ground2 {
      opacity: 1;
    }
  }
  .sun {
    width: @btnH * 0.25;
    height: @btnH * 0.25;
    top: 25%;
    left: 30%;
    background: #fefeec;
    &.sun2 {
      top: 83%;
    }
  }
}
.button {
  &:hover {
    .circle {
      transform: scale(0.93);
    }
  }
}
